A Very Brief History of the 12-Valve Cummins

If you’re a fan of big, North American pickup trucks, you’ve probably heard a thing or two about the Cummins diesel engine used in heavy-duty versions of the Dodge Ram. You may have even heard about what truck fans like to call the “12-valve”. To most people, more valves per cylinder would seem like a good thing. However, the 12-valve Cummins has achieved somewhat of a cult status in the truck scene. The 12-valve is as revered as the 2JZ or the K-series, and some people will even tell you that it’s the greatest engine ever made. Of course, you’re probably wondering why.

First of all, let’s talk about why it’s called the Cummins. The engine is made by Cummins, Inc. of Columbus, Indiana. Founded by diesel mechanic Clessie Cummins in 1919, Cummins has become one of the most respected diesel engine manufacturers in the world. Most of Cummins’ engines are used in heavy machinery, buses, transport trucks, and even as generators. There are few companies that know their way around a diesel engine like Cummins does.

So when it came time for Dodge to up the ante in the world of heavy-duty pickups, they turned to Cummins for help. General Motors had the ultra-efficient Detroit diesel, while Ford had the powerful IDI diesel engine made by International Harvester. Both of these engines were V8 diesels specifically designed for use in a pickup truck as an alternative to thirsty gasoline engines. In contrast, Dodge decided to borrow the existing B Series Cummins engine. The B Series was a straight-six diesel engine widely used in mail trucks, school buses and even in mining operations as generators. It needed to work in the Ram, too—Dodge was already several years late to the diesel truck party.

The first Cummins diesel to be fitted into a Dodge Ram was a 5.9-litre, 12-valve straight-six called the 6BT. From 1989 to 1998, the 6BT would cement its reputation as one of the greatest diesel engines ever made. Fitted from the beginning with a Holset turbocharger (which wasn’t intercooled until 1991), the “12-valve” became a legend for its power, efficiency, and reliability. The Cummins diesel helped usher in a new era of American trucks: never before had the humble pickup been able to work as hard as the Cummins-engined Ram. What made the Cummins so popular was the fact that its peak power and torque was insanely usable—in fact, the redline is only at 3,000 RPM! The 12-valve was able to get respectable fuel economy while producing torque figures never-before seen in an ordinary pickup truck.

By 1998, emissions regulations necessitated the switch from the 6BT “12-valve Cummins” to the ISB “24-valve Cummins”. Although the 24-valve was more powerful than the 6BT and was, by all means, still a very good engine, it never achieved quite the same popularity as the original 12-valve. Today, the 5.9 12-valve diesel is still very much sought-after by truck buyers for its reliability, mechanical simplicity, and efficiency. They are also very popular among enthusiasts, as the iron block can handle a lot of power. Mind you, because it’s essentially a scaled-down dump truck engine, this shouldn’t come as much of a surprise.

By now, I hope that I’ve been able to give you the impression that the 12-valve Cummins is a pretty good engine. But is it really one of the best engines ever made? I think you could make a pretty good argument in favour of the 6BT. From a tuning perspective, the 6BT was simple to work on, capable of handling huge amounts of power, and well-supported by both OEM and aftermarket parts manufacturers. If you could make a roadworthy brick shithouse, the Cummins would probably be the most fitting engine you could put in it. It might not set lap records at the Nurburgring, but if there’s a tree stump that needs to be pulled out of the ditch, a Cummins will probably get the job done.

This content was originally posted by a Car Throttle user on our Community platform and was not commissioned or created by the CT editorial team.